1. Field of the Invention
This invention relates to improvements in computer memory management. More particularly, this invention relates to the determination of the amount of available memory in a running computer application.
2. Description of the Related Art
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The Mobile Information Device Profile (MIDP) defines a set of Java application programming interfaces (APIs) that provide an application runtime environment for mobile information devices, such as cellular telephones. MIDP is defined in the document Mobile Information Device Profile (JSR-37), JCP Specification, Java 2 Platform, Micro Edition, 1.0a (Sun Microsystems Inc., Palo Alto, Calif., December 2000), which is incorporated herein by reference. MIDP builds on the Connected Limited Device Configuration (CLDC) of the Java 2 Platform, Micro Edition (J2ME). MIDP applications that use the MIDP and CLDC APIs are known as MIDlets.
Mobile information devices typically have a very small memory, low-speed graphics, and slow communications performance, when compared with personal computers (PCs). While programmers commonly develop applications using personal computers as development platforms, the memory and speed limitations of the target mobile information devices must be taken into account in order for the applications to run satisfactorily on the target devices. In particular, the memory capacity in mobile information devices is often a limiting factor in program development.
In early programming languages, memory allocation and deallocation was a burden imposed directly on the programmer, who was responsible to allocate and deallocate memory blocks. This burden was essentially eliminated over 40 years ago by the invention of garbage collectors, which are programs that deallocate memory that is assigned to dead or unreachable objects. Garbage collectors have greatly improved programmer productivity, and have enhanced software reliability. They are supported by modern programming languages, such as Java. A variety of different garbage collection techniques is now known in the art.
In general it is not possible for a garbage collector to determine exactly which objects are still live. It is commonly assumed by implementers of garbage collection routines that a live object is reachable or can be proven to be referenced. Nevertheless, the inability to guarantee that an object is live inconveniences a program developer who is working in an environment in which memory is a limiting resource. As supported in most languages, garbage collection is an asynchronous process. It is typically invoked automatically by the computer system at runtime when the amount of memory allocated by the running program reaches some limit, which depends on the amount of memory actually available in the system. Therefore, the developer is generally unable to determine at any particular point in the execution of the application how much of the memory allocated to the application is actually required, and how much is merely preempted by objects that are no longer reachable. Furthermore, it is often desirable to reduce the memory requirement of an application at critical points in its execution. At present, this cannot be done deterministically in the context of small wireless devices, such as cellular telephones, using current garbage collection techniques.